A method is known in prior art to be used for the manufacture of a built-in camshaft formed of a carrying tube and at least two working members consisting of longitudinal slots of rectangular cross section which are formed on the surface of a mounting opening of each working member (GB, A, 2210301). Then the working members (cams, bearing journals, eccentrics) are put on the tube in a predetermined sequence so that they are positioned at a required angular position, whereupon a mechanical expansion of the tube is carried out by applying a force thereto from the inside. In so doing, the outer diameter of the tube becomes larger than the diameter of the mounting opening in the working members, and portions of the tube fill up slots provided in the surface of the mounting openings. The expansion of the tube in the method of prior art knowledge is carried out by means of a tool shaped as a rod of circular cross-section with longitudinal projections on its outer surface. The number and section of the projections are therewith identical to the number and section of recesses in the mounting surface of the working members.
The method of prior art knowledge requires high precision in machining the mounting openings of the working members and essentially individual manufacturing of each component. Since the working members are set in a predetermined angular position on the tube, the arrangement of the slots in each working member and tube must exactly correspond to the arrangement of the projections of the tool. This need for high precision leads to a reduction in the productivity of assembly.
In addition to this, a method is also known in prior art to be used for the manufacture of a built-in camshaft (GB, A, 1117816), consisting a plurality of splines having essentially a triangular section and becoming narrower toward the vertex formed in the surface of mounting openings of each working member. The working members are placed on a tube in a predetermined angular and linear position and then the tube is expanded mechanically by applying a force from the inside of the tube until the splines are pressed into the body of the tube with their pointed vertices so that a permanent connection is thus formed between the working members and the tube. In this method of prior art knowledge, the expansion of the tube is carried out over the entire circumference of the tube using a tool . The tool consists of a rod and a working head attached at its end coaxially and defined by two conical surfaces. The bases of the two conical surfaces facing one another and having a cylindrical calibrating shoulder between them, which has a diameter corresponding to the inner diameter of the tube after its expansion. In order to ensure a guaranteed pressing-in of the pointed splines into the body of the tube over entire circumference, it is necessary to pull the tool through the tube with a high force, for instance, for tubes of 22 mm in diameter the pulling-through force is to be as high as about 18 tf. This puts a limitation on the selection of a material for the working member. The selected material must have an adequate ductility in order to avoid a failure of the working member in the process of pulling the tool through. At the same time, as a rule, more ductile materials, for instance steel, are hard to use and are not easily pressed. Therefore, in order to ensure the required precision of the products, a further finishing of the material by means of mechanical treatment is necessary which leads to a reduction in productivity and to an increase in the cost of production.